Twenty people were killed in the French Alps yesterday when a cable car taking staff, cleaners and maintenance workers to an international astronomical observatory fell 80 metres (260ft) to the valley below.

There were no survivors in the accident, which happened soon after 7.30am about a mile outside the village of St-Etienne-en-Dévoluy, near Gap in south-eastern France. The privately operated cable car was on its way up to the Pic de Bure observatory.

"It was a horrific sight," said Magali Espinasse, the local doctor's assistant, who was comforting victims' relatives.

"No one could have survived it and no one did. There were bodies scattered over a big area and there was almost nothing left of the cabin itself. It was like the aftermath of a plane crash."

The authorities confirmed that 20 bodies were recovered. "The cable car fell. We don't know why. These are working people and now they are dead," the mayor, Jean-Marie Bernard, said at a hastily organised crisis centre in the local tourist office.

"The mountains are in mourning today. Nothing could have led us to expect such a disaster."

Saying there had clearly been "a very serious malfunction", the state prosecutor, Michel Selaries, announced a manslaughter inquiry.

Investigators said they were examining a witness's statement that the cabin had nearly reached the peak before it began suddenly sliding back down the cable, gathering speed and plunging to the ground.

The French association of cable car operators said the accident seemed to have been caused by the cabin becoming unhooked from the cable rather than by the cable itself snapping.

"The system was built in the early 1980s and was in perfect working order," its spokesman said.

"It passed a safety inspection late last year and was really thoroughly serviced - like you would replace a man's heart and lungs."

He added that the incident was the worst cable car catastrophe in France's history.

The death toll equalled that of the disaster in the Italian resort of Cavalese in February last year when a US marine jet on a training flight severed the cable of a ski gondola.

At least five of the victims worked for a local building firm and came from St-Etienne, a ski and mountain-walking resort beneath the spectacular Pic de Bure plateau. They were on their way to carry out annual maintenance work on the research station, which is manned year-round by scientists from France, Germany and Spain.

Outside town hall, where counsellors and psychologists were comforting relatives, many of the village's 500 residents gathered silently in the hot sunshine. "I had friends among them," a grey-haired woman said as she was led weeping into the building.

Others said they were too upset to speak. "These mountain communities have a lot of heart," said Marcel Lesbros, a senator for the Hautes-Alpes region, who visited the village later in the afternoon. "Everyone here is personally touched by this."

The observatory is run by the Institut de Radioastronomie Millémétrique, a Franco-German research institute based in Grenoble.

The French president, Jacques Chirac, voiced his sadness at the weekly cabinet meeting in Paris and asked the government to send its condolences to relatives of the victims.

Arriving at the scene by helicopter, the interior minister, Jean-Pierre Chevènement, described the crash as "a truly horrible tragedy for a small, closely-knit mountain community".

It was the third big catastrophe in the French Alps this year. A huge avalanche swept 23 chalets away in two small hamlets near the ski resort of Chamonix in February, killing 12 people.

In March, a fire broke out on a lorry in the Mont Blanc tunnel, leaving 45 people dead.

 February 3, 1998 Twenty people die after a U.S. warplane hits a cable-car line in Cavalese in the Italian Dolomites, sending a cabin plunging 200 metres on to a mountainside.  January 1989 Eight technicians killed when car plunges 200 metres in Vaujany, France, during tests a week before it was due to go in to service.  February 13, 1983 Three cabins fall in Champoluc in Val d'Aosta. Eleven people killed.  March 9, 1976 Forty-two people die in Cavalese in world's worst cable-car disaster. One teenage girl survives, cushioned from impact of fall by bodies of victims. Inquest finds two steel cables crossed and one severed the other. Automatic safety system which could have prevented disaster was switched off.  December 8, 1970 Cable car falls between Bolzano and Merano in Italian Dolomites. Five people die.  December 25, 1965 Christmas Day power failure causes cabin to fall in Puy-de Sancy, France. Seven holidaymakers die, 10 more injured.  August 29, 1961 Military plane clips cable running between L'Aiguille du Midi and summit of Helbronner mountain in Alps. Three cabins fall. Five people die.